Observing at a prosthodontic practice

 Today Tom Giblin was kind enough to let me observe him for a day at his practice. I saw a full mouth case which was in the middle of preps and a few consultations and review appointments. Overall it was quite a relaxed practice and modern and advanced feel to the place. Below are some tips I picked up from the day:

When giving a block, give some LA with a short needle at the site and come back with a long needle with an aspirating syringe and the patient won't feel the block as much.

-The high speed air turbine is usually better than the red band as you can have some tactile feedback with the loss of torque. The power of the handpiece is relative to the air pressure and this can be turned up to reach the max speed of 400,000 RPM whereas redband handpiece has a max of 200,000 RPM. The only concern with the air pressure is damaging the internal chair lines but he hasn't had an issue with his chair.

-When packing cord, soak the cord in astringent but remove the excess by blotting it on a bib. Place the cord in a circle shape and grab both ends together and place it over the tooth with the free ends on the buccal to quickly arrange it for packing rather than holding one side of the strand and attempting to loop it around the tooth. The cord has some stretch so once the palatal and interproximal is packed, you can pull on the cord free ends to stretch it and gain extra length to finish off the buccal.

-Roll the cord packer down and provide outward pressure of the gingiva away from the tooth as you are trying to provide lateral displacement of the tissues.

-If the gingiva is excessively bleeding during preps, finish your rough prep, place astringent in a cotton pellet and pack that in with pressure on the gum and continue preps elsewhere.

-Optragate and Isolite in combination are very useful for isolation during long appointments. The isolite system has a bite block contralateral to the area you are working and a flap that loops around behind the arch you are working on with a lingual extension that holds the tongue out of the way with illumination and a built in suction. This holds the tongue and cheek out of the way, illuminates the area, and keeps it dry, and optragate retracts the lips.

-Sharp edges aren't ideal for scanning or milling but Tom doesn't use a disc but a wide diameter, red band cylindrical diamond gently around the occluso-axial line angle

-The prep appointment was a continuation of the previous appointment where he prepped the other side and made temporaries. Before this he bonded his mockup in with full surface etch and bonding with luxatemp. This allowed an immediate long term buildup which he can refine theocclusion of then scan as the template to make the final restorations. He prepped through this buildup and any remaining material he kept as the core of his restoration. Workflow of the prep appointment. LA, preoperative impressions for temporaries and as a back of in case the intraoral scan technology fails, preop intraoral scan of arches and bite, prep teeth (occlusal reduction, axial reduction), pack cord and hemostasis, finalise prep,retraction paste, high resolution scan of individual preps, scan of arches to coordinate scan of preps with preop scan, make temporaries and cement temporaries.

-Retraction paste is clay based with astringent. When in contact with water, the clay absorbs the water and expands to retract the gingiva

-The alginate substitute is essentially a cheap version of PVS so the benefit is that it is accurate and dimensionally stable so can be used as a pre op temporary restoration impression and can be kept till next appointment.

-Tom uses the preop impression as a full arch for greater seating and the handle makes it easier to hold and remove. He injects the temporary material into the impression and then onto the preps and seats the impression tray jiggling it as it goes down to seat the tray. Mark the midline of the impression with an instrument before injecting the material. While it is setting he uses the handle of the tray to lift and lower the temporaries. As it is multiple preps adjacent to each other it is unlikely to stay on the tooth but will stay in the tray. If the flash extends very far across the arch from where you're prepping it means the impression is very accurate.

-If it is a well fitting impression you don't need to do a lot of refinement as the flash will be very thin and can be torn off.  Remove the temporaries from the impression and with water spray over the sink use a flame bur to clean margins and make slices in the interproximal areas to open occlusal, buccal, lingual and gingival embrasures. Use a football bur to widen these slices and contour below the contact point.

Use bur at an angle into the tooth after cementation to remove any overhangs. The tip of the bur will be below the margin so dinging the tooth shouldn't be an issue if you are careful.

-He usually keeps one set of posterior teeth untouched as an unchanged reference allowing a positive spot for the temporary impression key and index for scanning

-When scanning the preps for a bridge he always includes the adjacent tooth and all teeth involved in the bridge to give more information for indexing the scan with the full arch scan.

-For bridge preps you have to make sure that the angulation of the buccal of one abutment is not interfering with the palatal of the other one. There should be no interference to path of draw.

-He often preps the margin first and goes back to straighten the axial walls to make sure there is no undercuts

-Prepping a canine he often does a knife edge margin on the distal as they tend to have a bulbous distal contour and prepping a heavy margin will cause excessive tooth structure removal.

-For added retention, endo-crowns i.e internal preparations increases the resistance form of the prep.  E.g if you need 2mm height for retention and the tooth is 1mm high, prepping 1mm vertical walls internally on the occlusal surface essentially makes 2 crown preps on the same tooth and increases resistance form.

-Onlay preps keep the non functional cusp side margin above the height of contour but take the functional cusp margin down further as it needs more surface area for bonding and more ceramic thickness in response to the shear forces on this cusp. The non functional cusp doesn't need too much ceramic as most of the force is on the braced functional cusp and down the central fissure where the restorations are often thin. Onlays give room for margin to be brought down further when the restorations have to be replaced and in erosion cases there is less enamel to begin with. 

-For posterior preps you can use shorter fatter burs as there is less room to work with. Fatter burs are less likely to cause ditching of the preps.

-After cementing the temporaries, seat them further by getting the patient to bite on a cotton roll. You can wait till it completely sets and remove the excess with a probe. 

-If the patient seats an implant retained over denture by biting down they are at risk of bending the locator inserts. Get them to use finger pressure to seat it. 

-If you open the bite in a patient with an existing implant crown you can remove the crown and get the lab to strip the porcelain back and add porcelain to the new bite but it may be easier and cheaper for them if they plan to have an RPD to put a locator abutment in as you can control the aesthetics of the tooth, not have optically different restorations next to each other and do away with a clasp

-When doing a trial mock up, put the stent it, leave it for a long time after set, use a flat plastic to remove the flash that is extruded from the stent as they are quite sharp and use the flat plastic to lift the flange of the stent to remove it. 

-Take 45 degree angled photos of the mock up as it is a more natural shot.

-"Screwmented" bridges are implant bridges with a screw retained abutment on one end and a cemented abutment on the other. These were used before angled abutments where if one implant was off axis it could be cemented on and the correct angulated one could be screwed down The issue with implants is that teeth move and wear whereas implants do not move and wear slower. As time goes by, the implants become higher in the occlusion so can be a reason for screws to come loose. If the screwmented bridge is high, the cemented portion will move and cement will washout and become loose. Then there is a large cantilever on the screw which loosens. Remove the screw and remove the bridge. Then clean up the cemented abutment, clean the cement out of the bridge and standblast with plastic ball polishing powder. Recement with temporary material e.g Fujitemp (washes out less) or temp bond and seat. when seating, screw the screw retained portion down to seat the bridge and remove excess cement.

-The screw is the fuse of the system or "canary in the coal mine" so if there are any occlusal issues the screw area will show the issue.